“Lithography” literally means stone writing, however the contemporary meaning is to produce a three dimensional image. “Photolithography” is a term that emerges with the discovery of photosensitive compounds used to define patterns on a printed circuit board. “Micro lithography” is a term used to describe small features using photolithography or photosensitive compounds for the manufacture of integrated circuits.
Semiconductors are manufactured using a photolithographic process. The micro lithographic process is the last step and goal in the formation of relief images. Photolithographic processes apply chemical solutions, such as photo-resist, antireflective coatings (ARC) and developer solutions, onto a surface of a semiconductor. The chemical solution is applied at the recommended film thickness to a wafer. For example, after the application of photo-resist onto the wafer, an image from a template, mask or reticule (hereinafter mask) containing clear and opaque regions is transferred into the photosensitive coating on the wafer surface using a projection system. The clear and opaque regions on the mask) correspond to the desired circuit pattern.
A projection system typically consists of the following optical components, a light source, a condensing lens, and an objective lens. The projection system is either stand-alone units, or they can be linked to a machine for dispensing photolithographic solutions, commonly known as track system.
A photo resists' lithographic performance is directly affected by the developer composition. The different photo-resist chemistries, in the exposed and unexposed areas are made either soluble or insoluble in a developer solution. The latent image formed by the exposure step is developed to form a relief image, corresponding to the desired circuit pattern.
Photolithography processes occur in a clean room or a temperature and humidity controlled environment, and track systems typically further include controlled chamber environment. In the example where the semiconductor is manufactured in a track system having a chamber environment, the chamber is typically circulated with highly filtered air. The semiconductor is moved within the track system among several different stations, by for example, a robotic arm. At each station, a different processing step is completed.
A typical coat/develop track machine or system 10 is illustrated schematically in FIG. 1. Here, a wafer 12 is moved with, for example, a robotic arm within the environmental chamber 14 of coat/develop track machine 10. Chamber 14 has constant airflow of filtered, humidity-controlled air. Machine 10 moves wafer 12 among several different stations/units.
For example, machine 10 moves wafer 12 to a first dispense unit 16. The first dispense unit 16 applies, for example, an antireflective coating onto the wafer 12. Next, machine 10 moves wafer 12 to a second dispense unit 18 where the photo-resist is applied to the wafer. It should be noted that on some coat/develop track machines 10 the antireflective coating and the photo resist are applied at the same coat bowl by different dispense units.
Wafer 12 is moved to a third station 20 where a bake or cure step removes residual solvent and anneals the film. Wafer 12 is then moved to a projection system 22 for the exposure process step. Here, projection system 22 is either linked to or stand-alone from machine 10. Projection system 22 exposed the coated wafer to some form of patterned radiation to create a latent image in the resist layer. The quality of the latent image is dependent on exposing hardware, the physics and chemistry of the interaction between the radiation and the resist, and in case of mask systems, the quality of the mask.
Finally, machine 10 moves the wafer 12 to a developer dispense station 23 where the developer is applied to dissolve the un-activated photo-resist.
Alternately, machine 10 does not move wafer 12 from station/unit to station/unit. Rather, machine 10 is adapted to move nozzles 24 coupled to each dispensing unit 16 and 18 to wafer 12 as needed. Nozzles 24 are commonly stored in a nozzle bath that prevents the nozzles from drying out and/or from becoming contaminated with extraneous particles.
For example, such photolithography coat/develop track machines 10 are commercially available from FSI International, TEL Incorporated, and such projection systems 22 are commercially available from ASM Lithography, Canon Corporation, and the like.
In order to increase the speed and capabilities of semiconductors, the circuit pattern on the wafer has been made smaller such that more circuit patterns are included on the semiconductor (i.e., higher density circuit patterns). Smaller circuit patterns mean that the resolution of the circuit pattern is typically on the order of sub-microns, and sub-sub microns, which requires precise dispensing of the chemical solutions described above.
Moreover, the techniques used for applying the chemical solutions to wafers 12 require precise dispensing of the solutions. Spin coating has long been accepted as a reliable method to coat wafer 12 with solutions of acceptable thickness, uniformity, adhesion, and defect levels. Spin coating is accomplished by flooding wafer 12 with an antireflective coating/resist solution and rapidly rotating it at a constant speed between 1,000 and 10,000 revolutions per minute until the solution is dry, leaving a thin film of the antireflective coating/resist solution on the wafer.
For example, two types of spin coating programs include dynamic spin coating and static spin coating. During dynamic spin coating, the desired amount of chemical solution is dispensed to the center of wafer 12 while it is spinning. However, during static dispense coating, the chemical solution is applied to the center of wafer 12 while it is idle, after the chemical application the wafer begins to rotate and spin until the film is dry. Such spin coating occurs in a coat bowl assembly 25.
Imprecise dispensing of chemical solutions onto wafer 12 leads to physical defects in the semiconductor produced from the wafer. Additionally, since micro lithography solutions are typically expensive it is important that the dispense units do not waste the chemical solutions.
Plumbed dispense units for coat/develop track machine machines 10 have been developed for the manufacture of semiconductors in large-scale production, namely where a large number of semiconductors are manufactured at a time, thus requiring large volumes of chemical solutions. Plumbed dispense units require long lengths of pipe or tubing from a remote reservoir of solution to the coat bowl assembly 25. For example, U.S. Pat. No. 5,527,161 to Bailey et al and U.S. Pat. No. 5,878,918 to Liao et al. provide such manufacturing scale, plumbed dispensing units. However, such plumbed dispensing units have proven too expensive, and inefficient for development or lab use, namely operations where a small number of semiconductors are manufactured at a time such as manufacturers of semiconductor grade chemicals for which extensive testing of its chemicals is required.